Superheterodyne receiver for unmodulated telegraphic signals



ay 3U, 19% D. KOFFYBERG 2,5U9flY7 SUPERHETERODYNE RECEIVER FOR UNMODULATED TELEGRAPHIC SIGNALS Filed July 29, 1948 D IEDERIK KOFFYBERG INVENTOR Patented May 30, 1950 SUPERHETERODYNE RECEIVER FOR UN- MODULA'IED TELEGRAPHIC SIGNALS Dlederik Koflyberg, Eindhoven, Netherlands, as-

signor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application July 29, 1948, Serial No. 41,363 In the Netherlands August 12, 1947 2 Claims.

The invention relates to a superheterodyne receiver adapted in particular for the reception of unmodulated telegraphic signals.

When receiving unmodulated telegraphic signals, it is known to convert them into audible signals by mixing the incoming signals with an auxiliary oscillation of substantially the same frequency. This results in the production of audible beat oscillations which may be fed to a reproducing device, for example, a loudspeaker.

In order to ensure in such a receiver on the one hand adequate amplification and on the other hand adequate selectivity, it is desirable to use a receiver comprising at least a tunable highifrequency amplifying stage, a mixing tube associated with a tunable local oscillator, an intermediate-frequency amplifying stage, a beat oscillator for producing auxiliary oscillations the frequency of which substantially corresponds to the intermediate frequency for the purpose of obtaining audible signals which correspond to the incoming telegraphic signals, and a lowfrequency amplifying stage.

However, the required number of amplifying tubes and the load of the receiver are thus comparatively high and this is a serious disadvantage for many uses.

The invention has for its object to provide a particularly advantageous form of receiver of the type outlined, in which while satisfying the requirements to be fulfilled the said disadvantages are obviated and in which, moreover, the amplifying tubes used in the said part of the receiver may all be of the same type, which is an important advantage in the case of replacing tubes.

According to the invention, use is made in such a receiver of three combination tubes each comprising two electrode systems having each a control-grid, for example, triode-hexodes of the type ECH 21, the electrode systems of the first combination tube serving for high-frequency amplification and low-frequency amplification respectively, those of the second combination tube acting as a mixing tube and for producing the local oscillations required and those of the third combination tube serving for intermediate-frequency amplification and for producing the auxiliary oscillations required for beat reception.

In order that the invention may be more clearly understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing, the single figure of which shows, by way of example, one embodiment of the receiver according to the invention.

by an aerial I are fed through a coupling coil 2 to a tunable oscillatory circuit 3 which is comprised in the control-grid circuit of a hexodeamplifier system 4 of a first combination triodehexode tube 5. The amplified oscillations abstracted from the anode circuit of the hexode part 4 are fed to a tunable oscillatory circuit 6 comprised in the control-grid circuit of a hexode 1 serving as a mixing tube. Together with a triode part 8 this hexode I is housed in a second combination tube 9, the triode part 8 of which is connected as a tunable local oscillator comprising a tuning circuit In. The intermediate-frequency oscillations set up across the anode circuit of the mixing hexode I are fed through. an intermediate-frequency bandpass filter l I to the control-grid of a heXode l 2 serving for intermediatefrequency amplification and forming part of a third combination tube [3. The triode part M of the latter combination tube serves to produce auxilliary oscillations of a frequency which substantially corresponds with the intermediate frequency (tuning circuit l5) These auxiliary oscillations are transmitted by the stray capacity between the control-grids of the triode and hexode parts to the control-grid of the hexode part and thus also amplified in it. The intermediate-frequency oscillations set up across the anode circuit of the hexode part I2 and the auxiliary oscillations of substantially the same frequency are fed through a bandpass filter it to a. detector diode |1,which forms part of a duo-diode-pentode l8. By mixing the intermediate-frequency oscillations and the auxiliary oscillations there is produced in the diode circuit an audible beat oscillation of, for example, 800 C./S, which is abstracted from the diode resistance I9 and, for the purpose of low-frequency amplification, fed through a coupling condenser 20 to the controlgrid of the triode part 2| of the first combination tube 5 of the receiver. The low-frequency oscillations amplified are abstracted through a coupling condenser 22 from the anode of the triode 2| and fed to the control-grid of the pentode part of the tube l 8, to the output circuit of which a loudspeaker 24 is connected through a transformer 23.

It has been surprising to find that with the above described method of connecting the combination tubes interfering couplings of the various amplifying stages remaining limited to a minimum value. For discoupling the high-frequency hexode 4 and the low-frequency triode 2| housed in the same tube it has been found sufficient to shunt the control-grid and anode re- The unmodulated telegraphic signals received sistances 25 and 25 respectively of the triode P by comparatively small discoupling condensers 21 and 28 respectively.

The amplifying systems, housed in the second combination tube 9, for mixing and for producing the local oscillations did not lead to undue coupling phenomena. It should be noted here that the use of a triode-hexode as a mixing tube and a local oscillator is known per se.

As for the third combination tube, it was founddesirable to make the amplitude of the auxiliary oscillations produced by the triode part l4 comparatively low, in order to avoid disturbing interference tones. This may be accomplished by tuning the triode oscillator l4, l5 to a frequency which substantially corresponds to a subharmonic of the intermediate-frequency oscillations, so that use is made of a higher harmonic of these oscillations to obtain the audible beat signals.

The receiver described may be provided in known manner with automatic gain control; for this purpose the oscillations occurring in the input circuit of the intermediate-frequency bandpass filter 16 are fed through a coupling condenser 29 to the second diode 30 of the duodiode-pentode l8. The diode resistance 3! has thus produced across it a control-voltage which is suitable for automatic volume control purposes and which may be fed, subsequent to smoothing (resistance 32, condenser 33) as a varying grid bias voltage to hexode 4, hexode I and hexode [2.

For the sake of simplicity the receiver is not shown to comprise changing-over of wave-band but as a matter of course the latter may be provided without inconvenience.

The receiver shown may be adapted not only to receive unmodulated telegraphic signals but also to receive modulated telegraphic signals and telephony by disconnection of the beat oscillator l4, ii; for this purpose the anode load of the said oscillator may include an interruptor 34.

Moreover, the receiver may be used not only for the purposes previously described, but, if desired, also for direction-finding of a transmitter, if the aerial l is replaced by a directional aerial system of customary type, for example a frame aerial. The high sensitivity that can be realized with the receiver described ensures accurate direction finding.

In the foregoing the resistances and associated discoupling condensers for the obtainment of the required operating voltages of the tubes are not described in detail. Suifice it to mention that the required negative grid bias voltages for the available amplifying systems are derived from cathode resistances shunted by condensers, whilst the anode leads of the various amplifying systems include the customary anode resistances and, as far as necessary discoupling condensers.

What I claim is:

1. A superheterodyne receiver for unmodulated telegraphic signals, comprising first, second and third electron discharge tubes of similar construction, each of said tubes comprising an envelope and within the envelope first and second electrode systems each comprising a cathode emission member, a control grid and an anode, a first circuit tunable to the frequency of said signals coupled to the control grid of the first electrode system of said first tube, a second circuit tunable to the frequency of said signals intercoupling the anode of the said first electrode system of said first tube and the control grid of the first electrode system of said second tube, means to couple the control grid and the anode of the second electrode system of said second tube in feedback relationship to produce an oscillator source. a third circuit tunable to the heterodyne frequency of said signal and said oscillator intercoupling the anode of the first electrode system of said second tube and the control grid of the first electrode system of said third tube, a fourth circuit tunable to a frequency substantially equal to said heterodyne frequency coupling in feedback relationship the control grid and anode of the second electrode system of said third tube to produce a beating frequency source, means to detect said heterodyne frequency and said beating frequency, means to couple said detecting means to the control grid of the second electrode system of said first tube, and output means coupled to the anode of the second electrode system of said first tube.

2. A superheterodyne receiver for unmodulated telegraphic signals, comprising first, second and third electron discharge tubes of similar construction, each of said tubes comprising an envelope and within the envelope first and second electrode systems each comprising a cathode emission member, a control grid and an anode, a. first circuit tunable to the frequency of said signals coupled to the control grid of the first electrode system of said first tube, a second circuit tunable to the frequency of said signals intercoupling the anode of the said first electrode system of said first tube and the control grid of the first electrode system of said second tube, means to couple the control grid and the anode of the second electrode system of said second tube in feedback relationship to produce an oscillator source, a third circuit tunable to the heterodyne frequency of said signal and said oscillator intercoupling the anode of the first electrode system of said second tube and the control grid of the first electrode system of said third tube, a fourth circuit tunable to a frequency substantially equal to said heterodyne frequency coupling in feedback relationship the control grid and anode of the second electrode system of said third tube to produce a beating frequency source, means to detect said heterodyne frequency and said heating frequency, means to couple said detecting means to the control grid of the second electrode system of said first tube, output means coupled to the anode of the second electrode system of said first tube, and heterodyne frequency filtering means shunting the control grid and emission member and the anode and emission member of the second electrode system of said first tube.

DIEDERIK KOFFYBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Lowell Mar. 19, 1940 Number 

